Making a cell for a motor-vehicle latent-heat storage unit

ABSTRACT

A motor-vehicle latent-heat storage unit is made by first positioning an elongated rectangular sheet-metal blank over a longitudinally extending slot formed in a die and then pressing an elongated anvil bar forming one of a pair of ultrasonic welding tools down against the blank over the slot to push the bar and the blank into the slot. This imparts to the blank a U-section and leaves longitudinally extending edge regions of the blank projecting out of the slot past the anvil bar. These edge regions are then folded transversely one after the other inward over the bar to form the blank into a tube with the edge regions overlapping each other. The other of the ultrasonic welding tools is subsequently pressed against the overlapped edge regions and therethrough against the anvil bar to ultrasonically weld together the overlapped edge regions along a full length of the tube. Finally the welded tube and the bar are moved longitudinally relative to each other to separate the tube from the bar.

FIELD OF THE INVENTION

The present invention relates to a motor-vehicle latent-heat storageunit. More particularly this invention concerns a method and apparatusfor making a cell or heat pipe for such a unit.

BACKGROUND OF THE INVENTION

A motor-vehicle latent-heat storage unit is typically provided betweenthe vehicle engine and the heating system and has a pack of cells orheat pipes each comprised of an elongated plate-shaped tube filled witha latent-heat storage medium. In a chemical-phase system the storagemedium is barium hydroxide and water (octahydrate) and the envelopesurround it is made of oxygen-free copper or nickel-plated steel. Forbest heat exchange the metallic envelope is only several tenths of amillimeter thick.

The main problem with these systems is that the cells are subject toconsiderable stresses. They are heated and cooled during normaloperation so that they will inherently expand and contract, and theinternal phase changes are responsible for further changes in volume.Similarly the liquid inside them will expand and contract so that theinternal pressure can vary quite a bit. Finally when employed in a motorvehicle they are subject to the dynamic shocks and stresses anything ina road vehicle has to withstand. Clearly it is difficult to build a cellthat is sufficiently thin walled to ensure good heat transfer betweenits contents and the heat-transfer fluid surrounding it yet strongenough to withstand the stresses it is subjected to during normal use.

Accordingly it is known from German patent document 4,036,392 to useseamless tubing to have an envelope of maximum strength. Unfortunatelymaking seamless tubing of the necessary thin wall thickness is extremelydifficult. In this system the procedure is complex since the seamlesstube is made from a flat plate of sheet metal into which an annularframe of a spacer tube is soldered. When the solder location is heatedthere are normally problems as the thin walls cannot withstandsubstantial pressure, as must be exerted by the iron during thesoldering operation.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide animproved method of and apparatus for making a cell for a motor-vehiclelatent-heat storage unit.

Another object is the provision of such an improved method of andapparatus for making a cell for a motor-vehicle latent-heat storage unitwhich overcomes the above-given disadvantages, that is which produces avery robust cell in a manner subject to low-cost mass production.

A further object is to provide an improved cell for a motor-vehiclelatent-heat storage unit.

SUMMARY OF THE INVENTION

A motor-vehicle latent-heat storage unit is made according to theinvention by first positioning an elongated rectangular sheet-metalblank over a longitudinally extending slot formed in a die and thenpressing an elongated anvil bar forming one of a pair of ultrasonicwelding tools down against the blank over the slot to push the bar andthe blank into the slot. This imparts to the .blank a U-section andleaves longitudinally extending edge regions of the blank projecting outof the slot past the anvil bar. These edge regions are then foldedtransversely one after the other inward over the bar to form the blankinto a tube with the edge regions overlapping each other. The other ofthe ultrasonic welding tools is subsequently pressed against theoverlapped edge regions and therethrough against the anvil bar toultrasonically weld together the overlapped edge regions along a fulllength of the tube. Finally the welded tube and the bar are movedlongitudinally relative to each other to separate the tube from the bar.

Ultrasonic welding in effect makes a seamless tube, as strong as onethat is extruded in one piece, because the weld unites the material at amolecular level. This is done without weldment, that is withoutinterposing solder or another material between the surfaces beingjoined, merely by fusing the two parts together. Since the surfaces aretightly pinched between the two tools it is possible to form a verystrong seam that can easily withstand the considerable stresses such acell is subjected to in use. Since the anvil is inside the tube, theconsiderable pressure brought by the sonotrode cannot collapse the tube.

The blank of this invention is made of technically pure andsubstantially oxygen-free copper or of nickel-plated steel. The bar hasa thickness of about 5 mm. The blank is at most a few tenths of amillimeter thick.

According to the invention after separating the tube from the bar anoutwardly concave plug is inserted into an end of the tube and solder isprovided in the tube end between the plug and the tube. Acomplementarily shaped press bar is positioned in the plug inserted intothe tube, and the end of the tube is laterally pressed against the plugand the plug is thereby pressed against the bar while heating the plugand the tube end to solder the plug to the end of the tube. Thiseffectively and solidly plugs the tube end. The plug and the tube are ofthe same material and the plug and tube end are heated inductively tomelt the solder. In addition the tube is cooled adjacent the tube endduring heating of the tube end and plug, preferably with an inert gas toavoid recrystallization of the metal. The plug is provided with a fillfitting.

The apparatus according to the invention has a die formed with alongitudinally extending and laterally open slot into which an elongatedanvil bar is fittable. This bar forms an ultrasonic welding tool and ispressed down onto an elongated rectangular sheet-metal blank positionedover the slot to push the blank into the slot, impart to the blank aU-section, and leave longitudinally extending edge regions of the blankprojecting out of the slot past the anvil bar. Slides are provided forfolding the edge regions transversely one after the other inward overthe bar and forming the blank into a tube with the edge regionsoverlapping each other. Another ultrasonic welding tool formed as aroller is pressed against the overlapped edge regions and therethroughagainst the anvil bar to ultrasonically weld together the overlappededge regions along a full length of the tube. The roller tool isprovided with a drive for rotating it and rolling it longitudinallyalong the tube on the overlapped edge regions. A controller rotates theroller at a predetermined peripheral speed and displaces itlongitudinally along the tube at a displacement speed equal to theperipheral speed. This controller compensates for wear of the roller byadjusting the speeds. The drive means for the bar includes at least onethreaded spindle extending transversely of the slot and threadedlyoperatively engaged with the bar. The bar is generally complementary tothe slot.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIGS. 1 through 8 are schematic diagrams illustrating the method of theinvention, with FIG. 6 being a section taken along line VI--VI of FIG.5;

FIG. 9 is a partly sectional detail view of an end of a pipe accordingto the invention;

FIG. 10 is a side view of an apparatus for carrying out the method;

FIG. 11 is a top view of the apparatus of FIG. 10;

FIG. 12 is a view like FIG. 11 but with the apparatus in a differentoperational position;

FIG. 13 is a section taken along line XIII--XIII of FIG. 12;

FIG. 14 is a view like FIG. 13 showing the parts in a differentoperational position; and

FIG. 15 is a partly sectional view of a detail of the apparatus.

SPECIFIC DESCRIPTION

As seen in FIGS. 1 through 8, a latent-heat storage cell or heat pipe 11is formed starting from (FIG. 1) an elongated rectangular sheet metalblank 1 that is laid atop two guides 8 flanking a slot 17 formed in adie 18. The blank 1 is made of oxygen-free pure copper and is at mostseveral tenths of a millimeter thick.

To start with as shown in FIG. 2 an anvil bar 2 some 5 mm thick ispressed down on the center of the blank 1 directly over the slot 17 toforce the blank 1 into it and transform it into a U-section intermediatepart 4 having a pair of edge regions 5 that project up out of the slot 2past the die 18. Then two tools indicated schematically at 6, which canin fact form the guides 8, are moved laterally in, one after the other,to fold the two edge regions 5 over and thereby form an overlap 7 shownin FIG. 3.

Then as shown in FIG. 4 another ultrasonic welding tool, a so-calledsonotrode 3, is engaged with the overlap 7 to form thereat alongitudinally extending integral weld 9. Such a weld is extremelystrong as it actually molecularly unites the two end regions 5. To formsuch a weld the tool shown schematically at 3 can be moved down towardthe other tool 2 or the latter can be moved up. Subsequently the bar 2is pulled axially out of the resultant tube 10 or the latter is pulledoff the bar 2.

The open end of the tube 10, shown in longitudinal section in FIG. 6, isthen closed by inserting into it a cup-shaped or U-section sheet-metalend plug 12 complementary to the end of the tube 10, that is of lozengeshape. A bead 13 of solder is provided all around the plug 12. Then ananvil 14 complementary to the outwardly concave shape of the plug 12 isfitted into it and heated soldering irons 15 are either pressed toeither side of the outside of the end of the tube 10 or run around it asindicated in FIG. 8 to melt the solder, pressing the end region againstthe anvil 14 to avoid deforming the tube 10. To avoid crystallization ofthe adjacent metal, a jet of a cooling protective gas can be directedfrom a nozzle 19 at adjacent regions of the tube 1.

FIG. 9 shows how the plug 12 is provided with a filling fitting 16, herea throughgoing tube. This fitting 16 is used to introduce thelatent-heat storage fluid into the tube 10 and is sealed permanentlyshut once the tube 10 has been filled.

FIGS. 10 through 15 show the apparatus for carrying out theabove-described process. This apparatus has a frame 110 on which ismounted a die 101 formed with an upwardly open slot 102 above which ispositioned a flat sheet-metal blank 103. A horizontally elongated bar104 forming an ultrasonic-welding anvil and of a shape complementary tothat of the slot 102 is carried on supports 121 and 122 threaded onupright pairs of spindles 119 and 120 that can be rotated by a driveshown schematically at 123 for vertical displacement of this bar 104.

Two folding slides 105 and 106 movable by actuators such as shownschematically at 124 serve to fold over upstanding edge regions 107 and108 of the workpiece 103 to form an overlap zone 109. Once the overlapzone 107 is formed, the two folding slides 105 and 106 are withdrawn andthe bar 104 is lifted to raise the now tubular workpiece out of the slot102.

Another ultrasonic welding tool 111 is constituted as a head 113 of arod 112 rotatably supported in a support 114 displaceable longitudinallyalong the slot 102 by a threaded spindle 116 rotated by a driveillustrated schematically at 125. A drive indicated schematically at 126in FIG. 15 rotates the head 113 at a peripheral speed identical to thatof longitudinal advance of the support 114 along the workpiece 103. Thetools 111 and 104 work together as the head 113 is rolled along theoverlap zone 109 in a welding location 115 to produce an ultrasonic weld117. A controller 18 operates the tool 104 and/or the tool 111 toproduce the weld, and to move the bar 104 upward as it erodes, asinevitable with such a welding operation. In addition the controlleradjusts the rotation of the rod 112 by the drive 126 as the head 113wears and its diameter increases, to keep its peripheral speed identicalto the tool-advance speed. The ultrasonic energy is normally produced bya piezoelectric or magnetostrictive oscillator in the sonotrode 11.

We claim:
 1. A method of making a cell for a motor-vehicle latent-heat storage unit, the method comprising the steps of sequentially:positioning an elongated rectangular sheet-metal blank over a longitudinally extending slot formed in a die; pressing an elongated anvil bar forming one of a pair of ultrasonic welding tools down against the blank over the slot to push the bar and the blank into the slot, thereby imparting to it a U-section, and leaving longitudinally extending edge regions projecting out of the slot past the anvil bar; folding the edge regions transversely one after the other inward over the bar, thereby forming the blank into a tube with the edge regions overlapping each other; pressing the other of the ultrasonic welding tools against the overlapped edge regions and therethrough against the anvil bar to ultrasonically weld together the overlapped edge regions along a full length of the tube; and longitudinally relatively moving the welded tube and the bar to separate the tube from the bar.
 2. The cell-making method defined in claim 1 wherein the blank is made of technically pure and substantially oxygen-free copper.
 3. The cell-making method defined in claim 1 wherein the blank is made of nickel-plated steel.
 4. The cell-making method defined in claim 1 wherein the bar has a thickness of about 5 mm.
 5. The cell-making method defined in claim 1 wherein the welding is made weldment-free.
 6. The cell-making method defined in claim 1, further comprising the steps after separating the tube from the bar ofinserting an outwardly concave plug into an end of the tube; providing solder in the tube end between the plug and the tube; positioning a complementarily shaped press bar in the plug inserted into the tube; and laterally pressing the end of the tube against the plug and the plug against the bar while heating the plug and the tube end to solder the plug to the end of the tube.
 7. The cell-making method defined in claim 6 wherein the plug and the tube are of the same material.
 8. The cell-making method defined in claim 6 wherein the plug and tube end are heated inductively.
 9. The cell-making method defined in claim 6, further comprising the step ofcooling the tube adjacent the tube end during heating of the tube end and plug.
 10. The cell-making method defined in claim 6 wherein the plug is provided with a fill fitting. 